Rice production in China has experienced two breakthroughs, application of dwarf varieties in the 1950's and hybrid varieties in the 1970's, and a new breakthrough of the super rice application in recent years, which involves construction of ideal plant type, usage of hybrid vigour, physiological-ecological regulation and other various theoretical innovations and technical practices. Each yield increase and quality improvement of rice is always accompanied by the alternative improvement of the source, sink and transportation, and continuous establishment of new type of source-sink relationship. Yield and quality of rice are actually determined in the process of accumulation and transportation and distribution of photoassimilates from “source” to “sink”, and depend on the intensity of source, sink and transportation as well as the interactive effects among them. Therefore, people often explore regulation methods and production technologies to achieve synchronous improvement of the yield and quality of rice from the aspect of source-sink theory.
“Source” refers to the organs that produce or output photoassimilates, such as leaves, stems and roots, among which the functional leaves and leaf sheaths are the main “source”. “Sink” refers to the organs that absorb and utilize photoassimilates or other nutrients, wherein grains are the main “sink”. “Transportation” refers to all transfusion tissues connecting the source and sink, currently, “transportation” is analyzed mainly from the aspects of anatomical structure of the panicle neck, the internode and the basal part of stem etc., as well as physiologically active substances. The source, sink and transportation are mutually connected and coordinated. The source provides photoassimilates to sink, the size and activity of the source affect the fullness of the grain sink; the feedback information from the sink regulates the activity of the source, the supply capacity of the source can be regulated by the needs of the sink, and the relationship between the source and sink is constantly balanced in dynamic changes; the situation of the transportation is also affected by the coordination degree of source-sink relationship to a large extent. Because of this, many physiological phenomena of source-sink relationship are still unable to be distinguished as primary or secondary, which are essentially as the result of mutual interaction between the source and sink. The effect of environmental factors and the regulation of cultivation measures affect the inner physiological and biochemical traits and apparent agriculture properties of plants by influencing the source, sink and transportation and their mutual relations during the growth and development of the plants, and the formation process of yield and quality.
Although the importance of source-sink relationship for high yield and good quality of rice is well known, no great progress has been made in the research on source-sink theory of rice until now. With the continuous development of rice production and further requirement for higher yield and better quality, the research on the source-sink relationship is unceasingly proceeding. However, there are still many problems to be further explored and solved, which is resulting from the limits of research method of the source-sink theory of crops. Generally, different ecological conditions (temperature and light, altitude, etc.) or cultivation regulation measures (density, fertilizer, etc.) are adopted to analyze the structure of source and sink and their mutual relationship among varieties, but environmental factors and cultivation measures themselves have net effect on the plant, with a reflection of “apparent source-sink relationship”. To solve the problem, the plants with different source level (leaf area) or sink level (spikelet number) under the same growth conditions can be compared. However, the isogenic line with true differences at the source level and sink level is difficult to be obtained genetically. Therefore, people can only adopt the means of manual leaf-cutting, spikelet-thinning and the like, or the methods of applying mutants, inducing (inhibiting) the activity of related physiological substance and so on, to purposefully increase (decrease) the source, increase (decrease) the sink and dredge (block) the transportation. By artificially changing the source-sink relationship of the original plants, some physiological indexes might be significantly changed, which facilitates the analytical comparison with control plants, thus becoming the most commonly used technical method for investigating source-sink relationship. But many studies have shown that most of the differences generated by these methods are induced. Not only the levels of source and sink are changed by these methods, but also other functions or components are induced to change, therefore inevitably resulting in physical injury or physiological interference to the plant and changing its natural growth characteristics. Furthermore, there are artificially selective errors on leaves, grains and other organs in the practical operation; thereby the real relationship and objective rule between the source and sink fail to be reflected accurately.
In summary, in the art, it is necessary to construct experimental systems suitable for the source-sink relationship study and technology methods that are able to effectively regulate the source-sink level.